$ E = \left[\begin{array}{rrr}1 & 0 & 2 \\ 1 & 1 & 2 \\ 2 & 2 & 1\end{array}\right]$ What is $ E^{-1}$ ?
Explanation: $ = \left[\begin{array}{rrr}1 & -\frac{4}{3} & \frac{2}{3} \\ -1 & 1 & 0 \\ 0 & \frac{2}{3} & -\frac{1}{3}\end{array}\right]$